Gun perforator and method of manufacture



May 6, 1958 L. SPENCER GUN PERFORATOR AND METHOD OF MANUFACTURE FiledAug. 18 1951 I a r hu Ftent 2,8332% Patented May 6, 1958 GUN PERFORATORAND IVEETHOD OF MANUFACTURE Lloyd Spencer, Los Angeles, Califi, assignorof sixty-six and two-thirds percent to Thomas C. Bannon, Altadena, Qalifand thirty-three and one-third percent to John D. Chesnut, NewportBeach, Calif.

Application August 18, 1951, Serial No. 242,489

Claims. (Cl. 102-20) My invention relates to gun perforators and methodof manufacture, more particularly to gun perforators of the expendabletype which utilize hollow or shaped charges to penetrate well casing.The present invention is a continuation in part of my copendingapplication Serial No. 3,674, filed January 22, 1948, now abandoned.

Included in the objects of my invention are:

First, to provide a gun perforator which utilizes hollow or shapedcharges, which is completely destroyed or disintegrated when fired, andwhich may be formed largely of material which is substantiallycompletely disintegratable or soluble in well liquids so as to minimizethe residue or rubble which must be bailed from the well, particularlyafter producing a large number of perforations.

Second, to provide an expendable gun perforator wherein the internal andexternal pressures are equalized so that the body of the gun perforatormay be relatively fragile and yet withstand the high pressures existingin a deep well.

Third, to provide an expendable gun perforator and method of manufacturewhich utilizes inexpensive and readily available material and permitsproduction either in large or moderate quantity at a particularly lowcost, so as to fully justify single use of each gun perforator.

Fourth, to provide an expendable gun perforator which is capable ofutilizing a liquid explosive and so arranged that the explosive may beadded just prior to lowering the gun perforator into the well bore, orat least after manufacture is completed, so that all manufacturingoperations, as well as storage are free from the presence of anexplosive, as well as avoiding the transportation of the gun perforatorin a loaded condition.

Fifth, to provide an expendable gun perforator which may be made ofmaterial having a density not greatly different from well liquids sothat the weight of the gun perforator need not be an appreciable factor,thus permitting the use of lightweight inexpensive surface equipment,even though a gun perforator may be made up to contain a large number ofperforating units.

Sixth, to provide a gun perforator which may utilize explosives havingrelatively high detonating pressures, above the strength of the gunperforator body when in air; then, by employing a firing meanssufficient to rupture the gun body, premature firing in air merelyruptures the gun body without detonating the explosive; however, whenthe gun body is suspended in a liquid surrounded by well casing, theresulting inertia of the system is sufficient to hold the gun bodyintact until detonation takes place; thus providing a gun perforatorwhich may be so constructed as to be incapable of operation unlesssubmerged in a liquid.

With the foregoing and other objects in view as may appear hereinafter,reference is directed to the accompanying drawings, in which:

Figure 1 is a fragmentary, partial sectional, partial elevational viewof one form of my expendable gun perforator.

Figure 2 is an enlarged transverse sectional view thereof taken through22 of Fig. 1.

Figure 3 is a fragmentary sectional view through 33 of Fig. 2.

Fig. 4 is a fragmentary sectional view through 4-4 of Fig. 1.

Fig. 5 is a transverse sectional view similar to Fig. 2 but showing amold employed in the manufacture of the gun perforator.

Fig. 6 is a fragmentary elevational view of a core structure employed ina modified method of manufacture.

Fig. 7 is a transverse sectional view analogous to Fig. 2 showing themanner in which core structures may be disposed for later casing withina gun body.

Fig. 8 is a fragmentary elevational view of a modified form of shellstructure. employed in the manufacture of a modified form of my gunbody, the view being taken along the plane 3-8 of Fig. 9.

Fig. 9 is a fragmentary bottom view of the shell struc ture.

Fig. 10 is an end view of the shell structure.

My gun perforator involves a gun body 1 of cylindrical form. Molded inthe gun body in a manner to be described hereinafter is a series ofhollow or shaped charge cells 2, each comprising a conical inner shell 3and a;

hemispherical, outer shell t. The two shells may be provided with matingflanges 5 which are sealed together. The shaped charge cells aresufficiently strong to withstand the submergence pressure to which thegun pen forator is subjected. To reduce the thickness of materialrequired or to increase the depth at which the cells may be submereged,they may be initially pressurized; for example with carbon dioxide.

Behind each shaped charge cell 2, the gun body defines a detonationchamber 6 which may be provided with a lining 7. The cells 2 are sealedwithin the gun body as will be brought out in more detail hereinafter.The chambers 6 are serially connected by a longitudinally extendingpassage 8 which may be provided with a lining 9. The upper extremity ofthe passage is enlarged to form a detonator cavity 10 which receives afiring or detonator element 11.

The upper extremity of the gun body is provided with mounting bolts 12anchored therein and arranged to attach the gun body to a weight bar 13or other means adapted for suspension from a cable, not shown. In thepresent instance the detonator 11 is indicated as of the electricallyfired type and provided with leads which extend through the weight bar13 and comunicate in a conventional manner with a conductor within thesuspension cable. However, it should be understood that other types ofdetonators and firing means may be used.

The lower extremity of the detonator passage is connected with anequalizer tube 14 open to the bottom of the gun body and adapted toreceive a plunger 15 which seals the lower end of the detonator passagesbut will displace axially under gradual change in pressure to equalizeapproximately the external and internal pressures.

The detonation chambers 6 and passages 8 as well as the cavity 10 andtube 14 are adapted to be filled with an explosive. The explosive ispreferably a liquid such as nitromethane sensitized with aniline.However, the explosive may be one capable of being poured into the gunbody when in a liquid state, even though solid at normal temperatures.For example, TNT may be used. It should be observed that under theconditions of use of a gun perforator the bottom hole temperatures maybe above the melting point of TNT.

In any case, the cavities of the gun body with the exception of thecavities within the conical cells are intended to be completely filledwith an explosive so that the gun body itself is not subjected to anyappreciable pressure dfierential between the interior explosive liquidand the exterior well fluids.

This is important for it is desired to construct the gun body ofinexpensive, friable and relatively weak material. in fact, a materialmay be used which when disintergrated by the explosive charge is solublein the well liquids; for example tar, asphalt, paraffines or waxeshaving a melting point above the well temperatures encountered may beused. This is of substantial advantage for wherever feasibleeconomically a large number of perforations are desired and thecumulative debris of a number of gun bodies requires expensive bailing.However, it is not mandatory that soluble materials be used, for thebody may be madeof plaster, cement or analogous, readily castablematerial.

Whatever the material selected, the method of manufacture of the gunperforator is essentially the same. A mold to is provided, which, forexample may take the form shown in Fig. 5. As it is desired for thehollow charges to be faced in different directions, the mold is dividedinto segments, in this case, three. The mold defines the prototype ofthe cavities desired in the gun body. The mold is so constructed thatthe hollow charge ceils may be secured therein at the radially outerends of what will later be the detonation chamber cavities.

The mold cavities are filled with a low melting metal alloy or othereasily castable material, so as to form a core 17. The resulting castingis then plated, if of nonconductive material, it is first coated withgraphite. The plating later becomes the lining 7 and 9 as well as thelining of the detonator cavity and equalizer tube. As will be broughtout more fully, hereinafter, the plating may be relatively thick (aboutone-sixteenth inch of copper) if the gun perforator is not to be usedsubmerged and a nitromethane type of explosive is used. However, if TNTis to be used or the gun perforator is to be fired submerged, a thinplating merely strong enough to permit handling in the course ofmanufacture is sufficient.

The plated core, or the plating with the core melted therefrom togetherwith the hollow charge cells is placed in a suitable cylindrical formand the material of the gun body cast therearound. The hollow chargecells are preferable in place during the plating of the core, as thisinsures a seal at the forward extremities of the detonation chambers. Inplace of plating, the core and the hollow char e cells may be spraycoated with fusible metal or a synthetic paint or analogous material.

The gun body may be provided with a reinforcing fabric sleeve 18,although it is desirable to avoid as much as possible substances whichmight later cause clogging of the well bore. Also the surface of the gunbody may be coated with a material to inhibit its solution in the wellfluids.

While the explosive may propagate its own detonation wave through thepassages of the gun body, propagation may be enhanced by use of adetonating cord 19, such as one containing PETN. Such cord is threadedthrough the passages as shown in Fig. 3.

It is highly desirable that the diameter of the gun I perforator be aslarge as possible to place the shaped charges as close as possible tothe well casing. Different size molds may be used to accomplish this, orthe passage forming portions of the core 17 may be bent to vary theradial spacing. If different axial spacing between detonation chambersis desired, correspondingly different molds are required.

While in Fig. l a single passage is shown connecting all. the detonationchambers serially, the detonation chambers may be divided into the sets,the members of each set occupying a common plane and being connected toa common passage. In this regard, reference is directed to Fig. 6wherein a core 20 is shown as compris- While it is desirable to employ acore and then coat the 7 mold to form a gun body cavity lining, it isfeasible to form the l nings by means of thin sheet metal stampings andconnecting tubes soldered or otherwise fabricated as shown in Figs. 8, 9and 10. In this case, complementary sheet metal shells 23 define thedetonation cavities. These shells clamp the hollow charge cells and areprovided with nipples 24 which receive connecting tubes 25. With thisarrangement, virtually any diameter of gun perforator or shot spacingmay be obtained.

It is, of course, desirable that in filling the gun perforator cavities,no air bubbles be entrapped. Thus it is desirable to provide a thin slitor small bleeder passage from the top sides of the detonation chambersto the passageways. Such means is indicated by 26 in Fig. 8 and a web 27to cast such bleeder passage is shown in Figs. 6 and 7. g

If the gun perforator is formed of an asphalt or analogous composition,it need not weigh appreciably more than the well liquid it displaces.Thus the submerged weight of the gun perforator may be virtually zero,and a weight bar employed to facilitate descent through the well liquid.Actually, the entire weight may be maintained so low that single strandmeasuring lines commonly used in oil wells may be used, and mechanicaldetonation employed. This is of primary importance, for the number ofshots which may be provided in each gun body may be few or great withoutappreciably influencing the travel of the gun perforator in the wellbore or require heavy and expensive surface equipment.

It is highly desirable that the gun perforator be safe to handle and,preferably, incapable of being fired unless within a well bore. If anexplosive such as sensitized nitromethane is used, the gun perforatormay be made so that it will not function unless submerged in liquid.This is made possible by the fact nitrornethane may be so sensitized asto require a predetermined degree of confinement in order to detonate.Thus if the gun body be cast of asphalt, cement or similar material oflow strength and the cavity linings be relatively thin, firing of thedetonator can be caused to only rupture the gun body, not developpressures therein high enough to detonate the explosive. However, if thegun perforator be submerged in a liquid, particularly when surrounded bya rigid well casing, the inertia of the system is such that the surrounding liquid functions as a solid during the extremely short periodrequired for detonation, consequently, the detonation pressures rise tothe required value and the gun perforator functions. Also, the increasedtemperature and pressure existing at the bottom of the well are factorsconducive to-detonation of the explosive at the bottom of a well withoutattendant hazard at the well mouth.

The equalizer tube and plug may be omitted if the lining of thedetonation chambers and connecting passages is yieldable and a gun bodymaterial capable of plastic flow is employed. In such case thesubmergence pressure may be transmitted directly to the explosivethrough the body and lining.

Having described certain embodiments of my invention, I do not desire tobe limited thereto, but intend to claim all novelty inherent in theappended claims.

I claim:

1. A gun perforator, comprising: a cast gun body of easily rupturablematerial defininga plurality of laterally directed detonation cavitiesandconnecting passages; a lining for said cavities and passages; andhollow shaped charge cells cast as inserts in said gun body at theradially outer ends of said detonation cavities; a continuous,uninterrupted body of a liquid explosive completely filling saidcavities and said connecting passages; and means at the upper end ofsaid gun body for causing that portion of said liquid explosive withinsaid passages to propagate a detonation wave through said passages pastsaid detonation cavities and to cause branching detonation of theportions of said liquid explosive wi hin said detonation cavities.

2. A gun perforator, comprising: a lining structure including aplurality of laterally directed detonation chamber cells and tubesintegrally connected to said chamber cells to join said chamber cells inseries thereby to form a single continuous cavity; a hollow submergencepressure resistant shell sealed in the outer end of each detonationchamber and including an end member extending into said detonationchamber and defining the focusing surface of a shaped charge; acontinuous, uninterrupted body of liquid explosive completely fillingsaid chamber cells and corn necting tubes and a gun body of easilyrupturable 1nale rial cast around said lining and hollow shells.

3. A gun perforator, comprising: a lining structure defining a pluralityof laterally directed detonation chambers and connecting passages andadapted to receive an explosive; a hollow submergence pressure resistantshell sealed in the outer end of each detonation chamber and includingan end member extending into said detonation chamber and defining thefocusing surface of a shaped charge; a gun body of easily rupturablematerial cast around said lining and hollow shells; a continuous,uninterrupted body of liquid explosive completely filling the spaceswithin said lining; and means for subjecting said explosive to thesubmergence pressures present when said gun body is submerged in aliquid.

4. A gun perforator adapted to be submerged to great depths in a liquidfilled well bore, comprising: a cast gun body of yieldable, easilyrupturable material defining a plurality of laterally directeddetonation cavities and connecting passages said gun body beingcollapsible when subjected to submergence pressures; hollow pressuresi'stant sealed shaped charge cells cast as inserts secured in theradially outer ends of said detonation cavities; and a continuousuninterrupted body of liquid explosive completely filling the cavitiesof said gun body, and subjected to submergence pressures applied throughthe walls of said gun body to support said gun body against collapse.

5. A gun perforator, comprising: a gun body formed of material solublein well fluids, and defining a plurality of laterally directeddetonating chambers and connecting passages forming a single continuouscavity; hollow submergence pressure resistant shaped charge cells sealedin the outer ends of said chambers; a continuous, uninterrupted body ofliquid explosive completely filling said detonation chambers andconnecting passages comprising said continuous cavity; said gun bodyadapted, on detonation of said explosive to be fragmentized whereby theresulting pieces may dissolve in the well liquids.

6. A gun perforator, comprising: a gun body formed of material solublein well fluids, and defining a plurality of laterally directeddetonating chambers and connecting passages forming a single continuouscavity; a continuous non-soluble for said cavity; :submergence pressureresistant hollow shaped charge cells sealed in the outer ends of saidchambers; a continuous, uninterrupted body of liquid explosivecompletely filling said detonation chambers and passage comprising saidlined cavity; said gun body adapted, on detonation of said explosive tobe fragmentized whereby the resulting pieces may dissolve in the Wellliquids.

7. A gun perforator, comprising: a plurality of hollow sealed shells,each including a shaped charge defining portion and a cap thereover,said shells adapted to Withstand the submergence pressures exerted byliquids within a well bore; and a frangible gun body cast completelyaround said shells with said caps imbedded within and located adjacentthe surface thereof, said gun body defining detonation chambers behindsaid shells and connecting passages joining said chambers and adapted toform therewith a single continuous cavity; and a continuous,uninterrupted body of a liquid explosive completely filling said cavityformed by said chambers and passages.

8. A gun perforator as set forth in claim 7 wherein: said gun is formedlargely of material soluble in well liquids, whereby, on detonation ofsaid explosive the resulting particles of the gun body readily dissolve.

9. A gun perforator as set forth in claim 7 wherein: anexplosive isemployed which requires, in order to detonate, a pressure surge abovethe bursting strength of the gun body whereby said gun body must besubmerged in Well liquids and utilize the inertia thereof in order towithstand a pressure surge of suflicient magnitude to cause detonationof said explosive, thereby rendering said explosive ineffective unlesssaid gun body is liquid submerged.

10. A gun perforator as set forth in claim 7 wherein: an explosive isemployed which requires, in order to detonate, a pressure surge abovethe bursting strength of the gun body whereby said gun body must besubmerged in well liquids and utilize the inertia thereof in order towith stand a pressure surge of sufiicient magnitude to cause detonationof said explosive, thereby rendering said explosive ineffective unlesssaid gun body is liquid submerged, said gun body being formed largely ofmaterial soluble in well liquids whereby on detonation of said eX-plosive therein the resulting gun body fragments are eventuallydissolved.

References Cited in the file of this patent UNITED STATES PATENTS1,239,247 Allison Sept. 4, 19.17 1,298,500 Hardel Mar. 25, 19191,777,153 Sanders Sept. 30, 1930 1,811,086 Kasch 1. June 23, 19312,394,400 Noles Feb. 5, 1946 2,473,722 Nelson June 21, 1949 2,494,256Muskat et al Jan. 10, 1950 2,543,057 Porter Feb. 27, 1951 2,587,244Sweetman Feb. 26, 1952 2,605,704 Dumas Aug. 5, 1952 2,669,928 SweetmanFeb. 23, 1954 FOREIGN PATENTS 618,618 Great Britain Feb. 24, 1949

